What things can affect the function of an enzyme?

Temperature, pH, concentration of enzymes, concentration of the substrate and concentration of any enzyme inhibitors.
Enzymes are large protein molecules that help to speed up reactions of substrates, molecules that are reacted. Because of their specific functions, enzymes have to have very specific shapes and chemical components, all in the right place at the right time, for maximum efficiency.
Temperature or heat energy can affect the functioning of an enzyme, as if there is too much energy the atoms forming the enzyme and substrate will shake about and bonds will break, meaning the enzyme becomes broken and useless. If there is too little energy, nothing can move about, and so substrates and enzymes rarely come into contact and the reaction will not happen frequently.
pH, related to the concentration of ##H^+## ions in a solution, can affect enzyme performance because if there is too much ##H^+##, the positive charges can interfere with hydrogen bonds inside the enzyme. This can cause the enzyme to change shape, resulting in the active site denaturing. (The active site is where the reaction happens, and denaturing means it stop working.)
Concentration of the enzyme can work to speed up rate of reaction, because if there are many enzymes, many reactions can happen at once. However, if there are more enzymes than substrates, then more enzymes become pointless, since all the substrates are already taken. There is a limit to how much you can improve reaction time by.
Concentration of the substrate affects time because if there is a lot of substrate in the environment, they will come into contact quickly with enzymes and the reaction rate will be greater. If there is too little substrate, it may take a lot of time for the enzyme to find the substrate.
Inhibitors are molecules that bond with enzymes and change their structure, denaturing the active site and inhibiting the enzyme from working. If there is a lot of enzyme inhibitor compared to substrate, i.e. there is a high inhibitor concentration, then the reaction will be slowed down as there is a high likelihood of a particular enzyme being inhibited before it can bond with a substrate, meaning nothing productive will react.